Witnessing the Birth of the Red Sequence: ALMA High-resolution Imaging of [C II] and Dust in Two Interacting Ultra-red Starbursts at z = 4.425

I. Oteo, R. J. Ivison, L. Dunne, I. Smail, A. M. Swinbank, Z-Y. Zhang, A. Lewis, S. J. Maddox, D. A. Riechers, S. Serjeant, P. van der Werf, A. D. Biggs, M. N. Bremer, P. Cigan, D. L. Clements, A. Cooray, H. Dannerbauer, S. Eales, E. Ibar, H. Messias, M. J. Michałowski, I. Pérez-Fournon, E. van Kampen

Exploiting the sensitivity and spatial resolution of the Atacama Large Millimeter/submillimeter Array, we have studied the morphology and the physical scale of the interstellar medium—both gas and dust—in SGP 38326, an unlensed pair of interacting starbursts at z = 4.425. SGP 38326 is the most luminous star bursting system known at z 〉 4, with a total IR luminosity of L IR ̃ 2.5 × 1013 L and a star formation rate of ̃ 4500 M yr-1. SGP 38326 also contains a molecular gas reservoir among the most massive yet found in the early universe, and it is the likely progenitor of a massive, red-and-dead elliptical galaxy at z ̃ 3. Probing scales of ̃0.″1 or ̃800 pc we find that the smooth distribution of the continuum emission from cool dust grains contrasts with the more irregular morphology of the gas, as traced by the [C ii] fine structure emission. The gas is also extended over larger physical scales than the dust. The velocity information provided by the resolved [C ii] emission reveals that the dynamics of the two interacting components of SGP 38326 are each compatible with disk-like, ordered rotation, but also reveals an ISM which is turbulent and unstable. Our observations support a scenario where at least a subset of the most distant extreme starbursts are highly dissipative mergers of gas-rich galaxies.

galaxies: high-redshift, galaxies: ISM, galaxies: starburst, submillimeter: galaxies

The Astrophysical Journal
August 2016

DOI: 10.3847/0004-637X/827/1/34
ADS Bibliographic code: 2016ApJ...827...34O